Abstract: The systematic risk evaluation of flood-control system is one of the most difficult and important issues in the domain of flood-control study.According to the system reliability theory,a failure sequence of flood-control system is defined,based on which,a systematic risk evaluation model for flood-control system is established.A general method for identifying the main failure sequences is advanced in algorithm form,and the main fault tree of flood-control system is built.Moreover,according to the characteristics of the systematic risk evaluation model,the identification algorithm is improved through the effective bounding measures,and the computational efficiency is improved largely.Finally,through an example,the study shows that the systematic risk attributed to an important structure is much less than the risk of the stucture itself because of the natural risk transfer and the artificial risk transfer.